West Nile Virus in Wildlife Michigan DNR Thomas M. Cooley Rose Lake Wildlife Disease Lab Michigan Department of Natural Resources

West Nile Virus: Reservoir Hosts Michigan DNR Isolated from numerous wild birds. Wetland and terrestrial species. Birds are primary amplifier hosts. Reservoir status not known. Migratory birds have a role in the distribution and re-introduction of virus into northern latitudes. Role of mammals is not known, but they appear to be dead end hosts.

In the United States: USGS Data Michigan DNR 194 Avian Species native/wild, 64 captive/exotic (38 Antibody positive) 28 Mammalian Species – 8 wild, 20 captive (7 Antibody positive) 2 Reptilian Species – 2 captive (1 Antibody positive)

In Michigan: Michigan DNR American Crow Blue Jay Common Raven Corvid Avian Species

In Michigan: Michigan DNR Non-Corvid Wild Avian Species Great Horned Owl Red-tailed Hawk Northern Goshawk Sharp-shinned Hawk Cedar Waxwing Ruffed Grouse Canada Goose House Finch Bald Eagle – diagnosed in Wisconsin Photo Credit: Dave Kenyon DNR

In Michigan: Michigan DNR Mammalian Species Eastern Fox Squirrel

Transmission Routes: Michigan DNR Naturally occurring - Transmission via mosquito bite. In captivity (research) – Transmission via fecal or oral secretions. Transmission via the eating of infected prey. It has not been proven that these 2 types of transmission occur naturally.

Clinical Signs: Michigan DNR Depression, anorexia (weight loss), dehydration, ataxia (loss of coordination), disorientation, inability to fly or use their legs, head tremors, eye twitching, apparent blindness, seizures/convulsions, abnormal head posture, circling, weakness, and death.

Michigan DNR Great Horned Owl diagnosed with WNV in 2002

Michigan DNR

Post Mortem Examination Michigan DNR Many organs are affected by the virus but in most cases appear grossly normal. The heart and kidney are collected for testing.

Post Mortem Diagnosis Michigan DNR Corvid avian species necropsies are performed at MSU’s Diagnostic Center for Population and Animal Health (DCPAH) Non-Corvid avian species and mammalian species necropsies are performed at the DNR’s Rose Lake Wildlife Disease Lab Testing is performed at MSU’s DCPAH

Gross Lesions Michigan DNR Gross lesions in birds are rare. Brain showing petechial hemorrhages. Intestine with pseudomembranous or necrotizing enteritis. Heart with tan areas of myocardial necrosis and myocarditis. Enlarged spleen.

Impact on Wildlife: Michigan DNR Reports of lower numbers of various avian and mammalian species have occurred but there is no evidence that this is or is not due to WNV. Appears avian populations may be impacted in isolated areas of the state, but not statewide.

Impact on Wildlife: Michigan DNR

Impact on Wildlife : Michigan DNR WNV may cause chronic infection in birds that reappears during times of stress. Birds may die of secondary organ damage in months or years following the initial infection.

Impact on Wildlife : Michigan DNR WNV may spread to the subtropics where species are stressed by habitat destruction and where year-round mosquito transmission would be possible. Endangered & threatened species may be impacted where the death of even a few individuals could be significant. WN ?

Testing of birds and mammals with central nervous system signs. Michigan DNR Testing until at least 2 positives per species are found in the state. Monitoring Impact on Wildlife:

Web-based submission of data and posting of results. Michigan DNR Tables & graphs: Summaries of dead bird and mammal reports. Summaries of test results. Monitoring Impact on Wildlife:

Michigan DNR